
No. 8951 



V s\ • 











—•-% /^^y^ >°/^w.°- a*^/** 






^ ° - ° <& 






VV 


















^°- 







'bv* 



v°V 















^% 


















V^ 1 







♦ v ^ 



,^- 























,\ 







***** 




?m&>^ "++$' •-^B'- "^1^ .""iSB^*- ^o<" ?-^iK- ^ov* 











v 












v ^. ; . 







, +_ 



*b? 



\^"'°A* 






A 9* 



a ^q* 



-.*• ^ 







* ^ 




O' 
























cv » 





• <W • 




^W 



• A v -X. - 







* ^ 









■» o 



*fev* 













+~ * 




«5°* - 









^°^ 




«5°< 



r •: 
















* <^ 






\y s • • j 




^ 




^o-« 










^0 o .0-/ 








Id 8951 



Bureau of Mines Information Circular/1983 




Bureau of Mines Coal Cutting 
Technology Facilities at the Twin 
Cities Research Center 



By Wallace W. Roepke, Carl F. Wingquist, 
Richard C. Olson, and Bruce D. Hanson 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8951 



Bureau of Mines Coal Cutting 
Technology Facilities at the Twin 
Cities Research Center 



By Wallace W. Roepke, Carl F. Wingquist, 
Richard C. Olson, and Bruce D. Hanson 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



Library of Congress Cataloging in Publication Data: 



'J air 



Bureau of Mines coal cutting technology facilities at the Twin Cit- 
ies Research Center. 

(Information circular / United States Department of the Interior, 
Bureau of Mines ; 8951) 

Bibliography: p. 24. 

Supt. of Docs, no.: I 28.27:8951. 

1. Coal mines and mining — Research— United States. 2. Twin Cit- 
ies Research Center. 3. Coal-cutting machinery— Testing. I. Roepke, 
Wallace W. II. Series: Information circular (United States. Bureau of 
Mines) ; 8951. 



TN295.U4 [TN805.A51 622s [622\33'4] 83-600212 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Facilities description 3 

Test equipment 4 

Small linear cutting system 4 

Large linear cutting system 6 

Ignition-wear-impact failure testing 10 

Vertical cutting linear tester 11 

Rotary drum wear-ignition tester 15 

Large sample test bay 17 

Microminer multiple-bit linear cutter 18 

In-seam tester 19 

Digital acquisition system 20 

Sample preparation 22 

Coal 22 

Synthetic samples 23 

Experimental design 23 

Summary 23 

References 24 

Appendix. — Specifications of major commercially available test equipment 

components 25 

ILLUSTRATIONS 

1. Coal cutting test facility building 3 

2 . Methane ignition test facility building 3 

3. Small linear cutting system 4 

4 . Uncut sample mounted in place 5 

5. Cutting in sample 6 

6 . Large deep cutter 7 

7. Test area of large cutter 7 

8 . Inner shroud around bit and dust sample part 8 

9 . Bit -dynamometer configuration on large cutter 8 

10. Bit mounting posts for use with dynamometer 9 

11. Samples after test cuts 10 

1 2 . Full-frame shot of shaper 11 

13. Fully instrumented sample holder on vertical shaper 12 

14. Sample test face-bit configuration 12 

15. Close view of bit-mount configuration 13 

1 6 . Typical bit-holder configurations 14 

1 7 . Automatic stepping equipment 14 

18. Rotary test facility showing drum and sample 16 

19. Control room with instrumentation for ignition testing 16 

20. Sample face showing increasing kerf length 17 

21. Sample face showing constant-kerf-length tests 18 

22. Frictional ignition test chamber milliseconds after frictional ignition... 18 

23. Microminer in large sample test bay 19 

24. In-seam tester in use underground 20 

25. In-seam tester cutting coal underground 21 

26. Face area underground after testing with in-seam tester 22 





UNIT OF MEASURE ABBREVIATIONS USED 


IN THIS REPORT 


°c 


degree Celsius 


kg 


kilogram 


cm 


centimeter 


kN 


kilonewton 


cm/min 


centimeter per minute 


lb 


pound 


cm/s 


centimeter per second 


m 


meter 


cu ft 


cubic foot 


m/min 


meter per minute 


cu m 


cubic meter 


mg 


milligram 


°F 


degree Fahrenheit 


mg/cu m 


milligram per cubic meter 


ft 


foot 


mm 


millimeter 


f t/min 


foot per minute 


um 


micrometer 


gal/min 


gallon per minute 


ym/s 


micrometer per second 


hp 


horsepower 


pet 


percent 


Hz 


hertz 


s 


second 


in 


inch 


rpm 


revolution per minute 


in/s 


inch per second 


W 


watt 


kHz 


kilohertz 







BUREAU OF MINES COAL CUTTING TECHNOLOGY FACILITIES 
AT THE TWIN CITIES RESEARCH CENTER 

By Wallace W. Roepke, : Carl F. Wingquist, 2 Richard C. Olson, 3 
and Bruce D. Hanson 



ABSTRACT 

Research on coal cutting at the Bureau of Mines Twin Cities Research 
Center (TCRC) has evolved from a purely mechanical approach, specifi- 
cally to reduce dust or frictional methane ignitions, into an under- 
standing of the complexity of the cutting system relationships. 
Achieving an understanding of these relationships requires a wide 
variety of testing techniques and equipment. Laboratory facilities and 
the associated equipment exist for shallow to deep cutting in both coal 
and coal-inclusive rock with any desired bit type. Research efforts 
with this equipment are providing insight for significant advances to 
help solve the problems of pneumoconiosis and frictional ignition. 
This effort will ultimately affect both respirable dust and methane ig- 
nitions at the face through better bit design and will increase the 
salable percent of run-of-mine (ROM) coal processed. It will also af- 
fect the design of rotary-drum cutting continuous mining machines 
(CMM) and longwall machines. 

This report describes the main features of the coal cutting research 
facilities at TCRC. 



^Supervisory physical scientist. 
2 Physicist. 
•'Mechanical engineer. 
^Physical scientist. 
Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 



INTRODUCTION 



The Federal Coal Mine Health and Safety 
Act of 1969 with revisions in 1977 
was enacted to insure healthier and 
safer working conditions. One require- 
ment, that airborne respirable coal dust 
not exceed 2 mg/cu m, is intended to re- 
duce the incidence of pneumoconiosis or 
"black lung" in coal miners. The enact- 
ment of this legislation, with its subse- 
quent monitoring and enforcement by the 
Mine Safety and Health Administration, 
required that the Bureau of Mines and 
others in the mining community better 
understand the mechanisms involved in 
generation and control of respirable 
dust. Accordingly, a continuing Bureau 
research program established in 1969 
has three broadly defined tasks directed 
specifically to pneumoconiosis: (1) con- 
trol of primary dust generation by cut- 
ting action, (2) secondary control of 
airborne dust, and (3) dust measurement 
instruments. 

Despite considerable insight into the 
dust problem and the body of opinion 
about the topic that existed before 
the Bureau's effort, no research data 
were available to specify the relation 
between the cutter(s) and respirable 
dust. Previous research was task ori- 
ented and did not cover the cutting sys- 
tem, 5 thus no relationship was drawn be- 
tween the cutting system and the total 
system. It has become apparent over the 
past several years that no single vari- 
able (e.g., dust, ignition, or wear) can 
be individually analyzed and yield usable 
results for direct field application. 
Accordingly, the TCRC laboratory incor- 
porates all aspects of cutter test- 
ing and is thus a fully integrated facil- 
ity that addresses both health and 
safety. 

5 The cutting system is defined herein 
as the cutter-mineral interface with 
all those variables affecting it: dust, 
wear, methane ignition, forces, cutter 
geometry, speed, etc. The total system 
is herein defined as the elements from 
the face through the preparation plant 
that support the cutting system. 



The original work at the Bureau's Twin 
Cities Research Center refined previous 
field efforts (_1_, 6)^ and provided labo- 
ratory confirmation that the reduction of 
dust came from a reduction of cutting en- 
ergy (9-19) . Additionally, the early ef- 
forts analyzed existing drum-type cutting 
by CMM's (14) . This early work indicated 
that a total cutting system design that 
correctly used coal cutting tools would 
substantially reduce respirable dust and 
frictional methane ignition. 

Those initial efforts have since been 
expanded to include the full spectrum of 
cutting system parameters. Testing can 
be done with either conical and radial 
cutters for CMM or larger longwall cut- 
ters on both coal and coal-inclusive 
rock. The test variables may include in- 
teractive or independent cutting bit 
forces, depth of cut, angle of attack, 
angle of skew, bit lubricity, primary 
respirable dust generation, symmetric and 
asymmetric bit wear, bit impact failure, 
and frictional impact ignitions. Only 
the facilities for these activities are 
described in this publication. Details 
of experimental designs, testing tech- 
niques , and research results may be found 
in the Bureau references listed. This 
research is looking at the fundamentals 
of the cutter-mineral interface and cut- 
ter design to solve specific problems of 
primary dust generation and frictional 
ignitions. It is long-term research and, 
as demonstrated by a number of patents on 
machine design (9^, 15-17) , may ultimately 
modify the equipment or the cutting meth- 
od to reduce the problems. The following 
discussion is intended to provide re- 
searchers, particularly those who are 
just becoming involved in rock and coal 
cutting research, with some insight into 
what is involved in setting up a compre- 
hensive test facility. Researchers in 
the private sector may also find it help- 
ful in identifying areas of mutual inter- 
est for possible cooperative efforts. 

^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendix. 



FACILITIES DESCRIPTION 



The equipment in the coal cutting tech- 
nology laboratory is in two separate 
buildings (figs. 1-2) in the Fort Snell- 
ing area of the Twin Cities Research 
Center. The smaller building contains 
only the system for frictional ignition 
testing, to isolate the potentially dan- 
gerous explosion area. The larger build- 
ing area contains sample preparation 



and storage facilities and all the other 
test systems. A general description is 
given in this paper of the equipment in 
each of these areas. 

The research in the laboratory in- 
cludes several areas, which sometimes 
overlap. At present these are cutting 
forces in three orthogonal axes , primary 




FIGURE 1. - Coal cutting test facility building. 




FIGURE 2. = Methane ignition test facility building. 



airborne respirable dust generation, 
bit impact failure, bit wear, and bit 
ignition potential in methane-air dur- 
ing cutting. Bits with various geom- 
etries and from various manufactur- 
ers in both new and used condition 



are used for the tests. Additional an- 
cillary test programs include water-bit 
lubrication, impacting bit, rotary bit, 
interface temperatures during abra- 
sion, new bit materials, and new bit 
designs. 



TEST EQUIPMENT 



The major equipment components include 
a small, horizontal, class C mill, a 
large planer mill, a large vertical 
shaper, a small research mining machine 
retrofit for multiple bit linear cutting 
(microminer) , a small, portable, in-seam 
tester (linear cutter) for in situ tests, 
and a narrow rotary-drum-bit ignition 
test stand. 

Ancillary support equipment includes 
multichannel recorders, strain-gaged 
plate and quartz crystal dynamometers, 
normal and high-speed 16- and 35-mm pho- 
tographic equipment, video recording 
equipment, programmable sample table 
stepping controllers, data acquisition 



systems , several optical particle coun- 
ters and/or sizers, several ionizer par- 
ticle counters , one piezo mass balance 
particle sizer, one electrical aerosol 
analyzer, 30 personal samplers, a 100-W 
C0 2 laser with power meter and pulse con- 
trol, two radiometers, and other miscel- 
laneous electronic equipment. 

SMALL LINEAR CUTTING SYSTEM 

The small linear cutting system with 
its associated Hewlett-Packard (HP) 7 

'Reference to specific products does 
not imply endorsement by the Bureau of 
Mines. 




FIGURE 3. 



inear cutting system. 



data acquisition system is shown in fig- 
ure 3. It is a modified, horizontal, 
simplex, class C mill with the following 
capabilities: 

1. Maximum sample size: 33 cm wide by 
25 cm long by 20 cm high. 

2. Traverse rate: 0.04 to 1.7 cm/s . 

3. Maximum depth of cut: 3.8 cm (1-1/2 
in). 

4. Peak forces: 18 kN (4,000 lb). 



It has a three-axis plate dynamometer, 
strain-gaged for X, Y, Z forces. 

The test bit is rigidly fixed to the 
dynamometer so the sample traverses under 
the bit. The arrangement for clamping 
the samples to a holder on the mill table 
is shown on the left in figure 4. Also 
shown, on the right, are the bit and the 
dust transport tube. This tube and the 
particle sampler are shown more clearly 
to the left of the cutter system in fig- 
ure 3. A typical test cut with a conical 
bit is shown in figure 5. 




FIGURE 4. - Uncut sample mounted in place. 




FIGURE 5. - Cutting in sample. 



The bit mount-dynamometer configuration 
is on the horizontal arms of the mill 
head, which permits the bit position to 
be varied laterally 22.9 cm (9 in) across 
any sample face. Depth of cut is ad- 
justed by vertical displacement of the 
mill head, since the horizontal arms that 
hold the bit's dynamometer can be moved 
up or down. The operating specifications 
of this mill are listed in the appendix. 



<10 cm/min) , and the signal bandwidth is 
accordingly narrow. The validity of 
testing at such low speeds is based on 
the fact that rock response to cutting is 
independent of speed within the range 
bounded by rate of creep on one end 
and rate of fracture propagation on the 
other. 

Dust produced by cutting is sampled 
just above the bit and carried by a low- 
loss tube through an isokinetic sampler 
to a modified Bausch & Lomb optical par- 
ticle counter (OPC). The OPC outputs, 
for each particle passing through its 
viewing area, a pulse whose amplitude is 
proportional to the particle's diameter. 
An HP multichannel analyzer (MCA) accepts 
the pulses as input and sorts them into 
classes to produce a size distribution 
histogram. 

LARGE LINEAR CUTTING SYSTEM 

The large deep linear cutting system is 
shown in figure 6. It is a planer mill 
which has been modified by removing the 
quill head and motor from the overhead 
rail and replacing them with a rigid 
mount to support the bit-dynamometer 
hardware. This overhead rail permits 
great flexibility in testing. The test 
area of the system is shown in figure 7. 
The bit-dynamometer mounting may be 
translated laterally across the total 
open throat distance of the table (176.6 
cm); the rail has a vertical displacement 
from 7.6 to 111.8 cm above the table. 
The wide throat, large, vertical clear- 
ance, and large table area (106.7 cm wide 
by 152.4 cm long) provide tremendous 
flexibility on sample size. 



Bit forces are fed through, and mea- 
sured by, a three-axis, strain-gaged, 
plate dynamometer which responds to lat- 
eral, normal, and cutting forces. Sig- 
nals from the three bridge circuits are 
fed to a hardware-controlled, HP data 
acquisition system. This system is capa- 
ble of high resolution (six-digit) mea- 
surements at relatively low speed (30 
channels per second) . The system is ade- 
quate for bit-force data whenever the 
cutting speed is relatively low (i.e., 



The long-way guides of the bed on which 
the table moves permit the table to be 
moved totally out of the throat area of 
the machine. A forklift or overhead 
hoist helps large sample handling. The 
center of figure 7 shows the test bit 
shrouded by plastic to eliminate back- 
ground dust. In the lower right corner 
one of the sample holders is shown 
clamped to the traverse table with the 
backing supports in place. The large 
tube above the shrouded bit brings clean 




FIGURE 6. - Large deep cutter. 




FIGURE 7. - Test area of large cutter. 




FIGURE 8. <■ Inner shroud around bit and dust sample part. 




FIGURE 9. - Bit-dynamometer configuration on large cutter. 



air into the outer shroud around the test 
area. A smaller, inner shroud surrounds 
the bit-coal test path (fig. 8). The op- 
tical particle-size pickup is mounted 
just above the cutting bit inside the in- 
ner shroud. The sampler itself, shown to 
the left of the clean air tube at the top 
center in figure 7, can cover a range 
from 0.2 to 20 ym; the used range is 0.2 
to 8 ym in five class intervals. 

A closer view of the bit-dynamometer 
configuration with the shrouds removed is 
in figure 9. The bits are mounted on 
5.08-cm-square posts 25.4 cm long which 
are clamped inside the dynamometer hous- 
ing; a bit is shown mounted in the left 
half of the figure. Additional bit-post 
configurations, in figure 10, give some 



idea of the adaptability of the system. 
The dynamometer is bolted to the support 
system shown in the upper right half of 
the figure. The support system has a 
5.08-cm-diam hinge pin which permits the 
bit-dynamometer package to be rotated for 
varying attack angles. Several coal sam- 
ples, after testing with this system, are 
shown in figure 11. 

The bit force dynamometer is a commer- 
cially built (Kistler) unit containing 
six pairs of one- and two-component, pi- 
ezoelectric, force transducers which re- 
spond in three mutually perpendicular 
directions. (See the appendix for the 
complete specifications.) The dynamom- 
eter outputs are connected to the charge 
amplifier by low-noise, armored, coaxial 




FIGURE 10. - Bit mounting posts for use with dynamometer. 



10 




FIGURE 11. - Samples after test cuts. 



cables. Voltage signals from the charge 
amplifiers are then input to the data ac- 
quisition system which may be the HP sys- 
tem described above but is more often a 
Digital M1NC (Modular Instrument Comput- 
er) system configured to condition, dig- 
itize, process , and store the data. A 
description of the Digital system itself 
will be found later in this report. 

The optical particle counter and multi- 
channel analyzer described previously are 
used to analyze the dust sampled. 



IGNITION-WEAR-IMPACT FAILURE TESTING 

Both the small and large horizontal, 
linear cutting systems are used to mea- 
sure primary respirable dust and orthogo- 
nal cutting forces, but these systems 
do not have an automatic cycle for bit- 
wear tests. Two appropriate systems are 
available. One is a constant-depth, ver- 
tical, linear cutter, and the other is 
a narrow rotary-drum section of a CMM. 
Since wear is so closely associated 
with frictional heating and ignition 



11 



potential, the ignition test facility in- 
cludes the rotary wear facility. 

Vertical Cutting Linear Tester 

The linear wear tester shown in figure 
12 is a modified large vertical slotter 
(or shaper) . This system has several 
different sample-holding configurations. 
The one in figure 12 is easy to use but 
measures normal force only. Figure 13 is 
a closer view of a fully instrumented 
system that measures orthogonal forces 
and rotary bit motion during cutting. 
This system requires substantially more 
time per test set owing to its complex- 
ity. The amount of data recovered with 
it also requires sophisticated, ancillary 
equipment. 

In the vertical test system the bit is 
mounted on the ram, which moves while the 
sample is stationary. The sample test 
face and bit configuration after testing 
are shown in figure 14. A closer view of 
the bit-mounting configuration is shown 
in figure 15. The potentiometer at the 




FIGURE 12. - Full-frame shot of shaper. 



back end of the bit mounting block is 
part of the bit-rotation measurement 
package. 

Several additional bit-holder configu- 
rations are shown in figure 16 to demon- 
strate flexibility on (from left to 
right) attack angles, skew, and/or bit 
type. The tool post holder in which a 
bit and block are mounted automatically 
retracts the bit at the end of each pass 
so the bit is not dragged in reverse 
through the test sample on the return 
stroke. 

The slotter table has been modified to 
permit automatic stepping up to 5.08 
cm between test cuts. This automatic- 
stepper control system is shown in figure 
17 at the left side of the fully instru- 
mented, sample-holding fixture. A re- 
versing feature has been incorporated in 
the automatic cycle so at the end of any 
set of face cuts the system pauses one 
stroke after the last cut, the sample is 
automatically stepped forward to estab- 
lish the required depth of cut, the table 
reverses itself, and the testing contin- 
ues in reverse across the face. The pro- 
cedure automatically continues in this 
manner back and forth across the face, 
using predetermined spacing and depth of 
cut, until the programmed number of cuts 
has been made. With this system long- 
term wear testing may be conducted un- 
attended. Since wear only occurs with 
harder inclusive materials, this system 
is not used for cutting clean coal and, 
therefore, has no dust sampling attached 
to it. It would be easy, however, to 
shroud the test area and obtain dust sam- 
ples should it ever be worthwhile. 

Force in general, but especially normal 
force, has been shown to change rapidly 
with wear (4_, 10) . Therefore this system 
has been designed to measure either 
normal force alone, when easy and rapid 
testing is desirable, or orthogonal 
forces, when a complete data set is 
necessary. The sample mounts are gauged, 
not the bit holder, as on the previously 
described systems. The fully instru- 
mented sample holder has been designed to 
use four, triaxial, quartz-crystal load 



12 




FIGURE 13. - Fully instrumented sample holder on vertical shaper. 










FIGURE 14. - Sample test face-bit configuration. 



13 




FIGURE 15. - Close view of bit-mount configuration, 



cells mounted between the four supporting 
arms of the sample holder and the four 
support plates on the table's mounting 
frame. The design keeps the load cells 
within ±5.08 cm of the plane of the bit- 
mineral interface to limit torque loading 
on them. Two of the support plates may 
be seen on the left in figure 17, and the 
inside edges of two of the support arms 
are at the right center of the same fig- 
ure. The loads cells are captive between 
these four points. 

The X, Y, and Z outputs from the load 
cells are summed (connected in parallel) 
to yield the lateral, cutting, and normal 



bit forces, respectively. Because of the 
relatively high cutting speeds of this 
machine, the frequency content of the bit 
force signals can reach 1,000 Hz or high- 
er. Therefore, to achieve high-fidelity 
data recording, a multichannel, FM tape 
recording system is employed. By record- 
ing at high tape speed and replaying at a 
low speed, the time base is expanded, 
making it possible to produce accurate 
strip chart recordings. By expanding 
this time base, the speed limitations of 
the data acquisition system (MINC) are 
also overcome. Several additional data 
tracks are available for recording other 
quantities such as bit rotation, dust 



14 




FIGURE 16. - Typical bit-holder configurations. 




FIGURE 17. - Automatic stepping equipment. 



15 



concentration, acoustic noise, and bit- 
rock interface temperature. The latter 
measurement is through a high-speed (lOys 
response) noncontacting radiometer which 
covers the range from 800° to 3,000° C. 

Rotary Drum Wear-Ignition Tester 

The rotary wear facility is shown in 
figure 18. This system has a multiple 
use since it incorporates wear, impact 
failure, and ignition testing in the same 
facility. The major components in the 
system are the full 86.36-cm (tip-to-tip) 
drum section and the sample mounted on an 
automatic, remote-controllable X-Y table. 
Not shown in this figure, but directly 
behind the chamber on the left, are a 
motor and pump for driving four motors 
mounted on the drum section. Two of the 
motors may be seen on the left in figure 
18. The other two, out of view, are on 
the opposite side of the drum. Figure 19 
shows the control and instrumentation 
system in an adjacent room. The test 
facility has the following specific 
capabilities: 

1. 100-hp, 100-gal/min pump and motor 
driving four Staufa motors on a 15.2- 
cm-wide, single-bit row; 86.4-cm-diam CMM 
drum section rigidly mounted to the cham- 
ber base. 

2. 0- to 100-rpm infinitely variable 
drum speed. 

3. Maximum sample size of 2.832 x 10" 2 
cu m (1 cu ft) . 

4. Sample mounted on an X-Y base power 
driven in each axis by stepper motors 
programmable and remotely operated from 
the control room. 

5. 0- to 0.95-cm/s advance rate to 
move sample into bit in Y-axis for in- 
creasing arc length-kerf depth tests. 

6. 0- to 4.45-cm/s lateral rate to 
translate sample past bit in X-axis for 
constant arc length-kerf depth tests. 

During all methane ignition, impact 
failure, and wear testing, it is routine 



instrumentation procedure to monitor cut- 
ting (tangential) force, work performed 
per impact, cutterhead speed; and for ig- 
nition testing, percent CH 4 in the test 
chamber is also monitored. These data 
are recorded on a multichannel strip 
chart recorder. 

Cutting force is recorded from a dif- 
ferential pressure transducer connected 
across the hydraulic motors that drive 
the cutterhead. The pressure drop across 
the motors is related to the torque at 
the cutterhead. This relationship has 
been established by calibration with a 
load cell. 

Work performed, or energy absorbed per 
impact, is determined by electronically 
taking the time integral of the cutting- 
force signal and multiplying this result, 
the impulse, by the cutting radius and 
angular velocity of the cutterhead. 

Angular velocity, or revolutions per 
minute, is monitored by a magnetic gear- 
tooth sensor in proximity to a drive 
gear. The sensor's pulse output drives a 
f requency-to-dc converter, which in turn 
drives an rpm-scaled meter and a recorder 
pen. 

Methane concentration is monitored con- 
tinuously by a methanometer within the 
test chamber. This sensor is basically a 
wheatstone bridge in which the tempera- 
ture and, therefore, the resistance of 
one of the arms depend on the concentra- 
tion of methane in the atmosphere. The 
bridge signal is amplified to drive a 
meter movement and one channel of the 
recorder. 

During any test the cutter tool mounted 
on the drum section rotates at the set 
speed. The sample is then stepped into 
the cutter at a predetermined advance 
rate for an increasing kerf depth and 
length, i.e., trimming top rock (fig. 
20) , or set to a certain depth and 
stepped across the face of the drum for 
multipass, constant kerf depth and length 
cutting, i.e., sumping along top rock 
(fig. 21). When the system is being used 
for bit-impact failure tests, only half 



16 




FIGURE 18. - Rotary test facility showing drum and sample. 




FIGURE 19. - Control room with instrumentation for ignition testing, 



17 




FIGURE 20. - Sample face showing increasing kerf length (i.e., trench cut with fixed depth of ad- 
vance, same cut each pass). 



the sample height is used so the bit will 
impact the top face of the sample at max- 
imum depth of cut, i.e., to simulate the 
middle band material. For wear testing, 
the system may be set to automatically 
cycle back and forth across the test face 
in the same manner as the vertical slot- 
ter until a set number of cuts have been 
made at the preset depth and spacing. 

For use as a frictional ignition facil- 
ity, the chamber is sealed across the 
open side with polyethylene sheeting, an 
easily ruptured diaphragm that quickly 



vents the chamber on ignition. Ignitions 
are vented harmlessly to a fenced area 
outside the building. Figure 22 shows 
the chamber just a few milliseconds after 
an ignition with the diaphragm already 
rupturing along the bottom edge. Results 
of recent bit ignition tests may be found 
in references 3 and 7. 

LARGE SAMPLE TEST BAY 

The large sample test bay with the 
microminer in place is shown in figure 
23. The bay is constructed of 30.48-cm 



18 







Ilillslal 












llll 111 






m 






'■':'■ i ■ 






! i V l > 


^BSSVs Sws w» m 




HFiI i ft & f Pi P 




i 


■lllflrJifl 


1^ 


' * . * 




: *i 


* : i' i I 






I f I 


■ Iffln I m * § f ( f : 






£ I f 1 1 f 1 § 




HHilili 




till ill 




.^ a aK S ■ :;w -M M $ 



FIGURE 21. - Sample face showing constant-kerf- 
length tests (i.e., transverse cut with fixed depth of 
cut, new cut each pass). 




FIGURE 22. - Frictional ignition test chamber milli- 
seconds after frictional ignition. 

structural I-beams with horizontal beams 
cemented in the floor between the up- 
rights in the same manner as the top 
crosspieces to form a box shape. Such 
an arrangement provides stability for 
locking the microminer or any other test 
apparatus in place during tests. The 



sample support section, shown on the 
right side of figure 23, has two horizon- 
tal crosspieces mounted between U-shaped 
brackets on the uprights and held by 
5.08-cm pins. These provide the backing 
for the normal forces imposed upon the 
sample during cutting. The horizontal 
cutting force is supported by the steel 
beam in the floor to which the uprights 
are welded. 

A simulated coal material has been de- 
veloped for this test bay since it is not 
practical to obtain coal in the sample 
size necessary. A complete description 
of this synthetic material is contained 
in a following section. 

Although respirable dust measurements 
cannot be directly obtained from the sim- 
ulated sample, relative differences can 
be obtained by shrouding the entire 
test bay and mounting a quick response 
sampler inside the cutting area. To ob- 
tain cutting forces either the test 
equipment or the sample support system 
must be instrumented. This large test 
bay is presently used with two systems: 
the linear cutting retrofit microminer 
and the in-seam tester. 

Microminer Multiple-Bit Linear Cutter 

The original research microminer (6) 
has been modified by replacing the nar- 
row, rotary drum section (now being used 
in the ignition-wear test facility) with 
a multiple-bit head which makes linear 
cuts (fig. 23). The machine is designed 
for deep linear cutting with multiple 
bits. One of the bit mounts is instru- 
mented to obtain orthogonal cutting 
forces. In use, the machine is trammed 
and locked into position in the test bay 
by front and rear roof jacks. The rear 
roof jacks have a canopy to cover the 
operator's station. In the bay these 
roof jacks are set against the cross 
beams that simulate the top and lock the 
machine in place. The bit-block mounting 
combination is designed for a maximum 
12.7-cm depth of cut over a maximum ver- 
tical distance of 198 cm. 



19 




FIGURE 23. = Microminer in large sample test bay. 

Bit force instrumentation consists of Assembled size: 

three strain-gaged clevis pins which at- Length 50 in. 

tach the bit mounting block to the four- Width 18 in. 

bar linkage that retracts and extends Height 42 in. 

each bit. The bridge outputs are re- Assembled weight 250 lb. 

solved into components of normal and Hydraulic power required at 

cutting force and summed electronically. 1,500 psi: 

The data are available as analog outputs Face preparation 10 hp. 

or digitally in binary coded decimal Test cuts 2 hp. 

(BCD) form. Power for instruments Battery 

Maximum cutting force 3,000 lb. 

In-Seam Tester Maximum cutting length 20 in. 

The in-seam tester (1ST) (fig. 24) is a Additional supporting equipment (packing 
Bureau-developed portable device that can cases, spare parts, hydraulic rotary im- 
be carried to an underground face for pact drill, etc.) adds 250 lb to the to- 
measuring orthogonal cutting forces in tal system. The heaviest single item, 
situ (fig. 25). Additionally, the device the cutter with hydraulic cylinder and 
has a shroud that can be used with a supporting structure weighs 150 lb. 
rapid-response optical particle sizer to 

obtain primary dust data. This total Bit forces are fed to the support 

system provides direct laboratory-field structure through a splined shaft instru- 

test correlation since portability takes mented with strain gages to measure 

it to any environment. An underground normal and cutting force. A portable 

face after cutting with the 1ST is shown data acquisition system digitizes and 

in figure 26. Specifications of the unit stores the data, which are then read 
follows: 



20 




FIGURE 24. » ln°seam tester in use underground. 



out as a time-at-load-level histogram. 
Energy, mean force, and peak force can 
be determined from the histogram. 

It is anticipated that data produced 
with the 1ST will enable designers to 
select pick types, spacing, lacing, depth 
of cut, and rotary speed for specific 
coal types and seam conditions to improve 
cutting performance. In preliminary 
field tests already completed, one 



operator indicated a 15-pct increase in 
productivity by reorienting direction of 
cutting in the seam. While the Bureau is 
not yet ready to make such claims, since 
the device is still a research tool, it 
is already apparent the 1ST has great po- 
tential for helping operators improve the 
coal-machine interface to properly match 
machine characteristics to the seam 
characteristics . 



DIGITAL ACQUISITION SYSTEM 



A Digital MINC II system is available 
for data acquisition, processing, and 
storage. The system is based on the 
PDP-11/23 8 processor with the KEF11 
floating-point chip. Peripheral storage 
is provided by a dual drive RX02 floppy 

8 The terms "PDP," etc., are the manu- 
facturer's terminology and have no 
spelled-out equivalents. 



diskette system and a dual-drive RL02 
hard disk system. A total of 21 M bytes 
of random access storage is provided. 
User interaction with the system is 
through a VT105 video graphics terminal. 
Hard copies of video displays can be made 
on a Tektronics model 4632 device. In- 
terfacing with the system is accomplished 
through RS232C ports, an IEEE instrument 
bus, and MINC input-output modules. 



21 




FIGURE 25. • ln=seam tester cutting coal underground. 



22 




FIGURE 26. - Face area underground after testing with in-seam tester. 



The modules presently include an A/D con- 
verter, a preamplifier, and a program- 
mable clock. The system operates on MINC 



basic V.2.0, which includes routines for 
data acquisition and analysis, graphics, 
and IEEE bus support. 



SAMPLE PREPARATION 



COAL 

The need for a constant supply of test 
samples requires both field acquisition 
and synthetic coal preparation. Field 
samples are sent to the Bureau; each is 
usually encased in gypsum for easy stor- 
age and handling, and to allow a stiff 
mounting in the cutting fixture, or to 
hold it at the proper bedding plane ori- 
entation. The coal soon changes from its 
in situ condition after it is left 
exposed in the laboratory environment. 
For further protection, the encased coal 
is stockpiled in a 90-pct-humidity room; 
as an alternative, raw coal may be im- 
mersed in water until needed. It will 



then be encased in gypsum 15 to 30 days 
before testing. Gypsum is used as the 
encapsulating material because the form 
used neither contracts nor expands on 
setup, which prevents adding unknown tri- 
axial loads to the sample. 

The coal to be encased in gypsum usu- 
ally must be trimmed with a wire saw to 
fit in one of the forms. Those samples 
immersed in water are not trimmed for the 
form until they are ready to be used. 
When a coal sample is going to be used 
for cutting tests, one face of the gypsum 
block is cut off about 1 in back, and the 
block is turned 90° and sawed lengthwise 
down the center. The coal is then held 



23 



in a gypsum block with flat sides and 
ends for rigid mounting in the test fix- 
ture, but the top and front face are open 
for test cuts at the proper bedding ori- 
entation. The coal samples are usually 
not cut open until the day before test- 
ing. New raw coal is obtained about ev- 
ery 6 months. 

SYNTHETIC SAMPLES 

To perform full-scale cutting tests in 
the laboratory , large coal samples would 
be required. It is not practical to ob- 
tain such samples since they tend to 
break during acquisition or transport. 
Also their acquisition disrupts mine 
operation. Large samples also tend to 
deteriorate rapidly in the laboratory. 
Simulated coal avoids all of these diffi- 
culties. It is made in blocks shaped to 
fit the test facility. Unlike coal, they 
have a uniform matrix, which allows for 
consistent testing. The best simulation 
material found to date is a modified gyp- 
sum or plaster mix. 



The physical characteristics of simu- 
lated coal are wide ranging, so the mate- 
rial can be tailored for specific charac- 
teristics. The strength can be varied by 
varying the mix. By reducing the mixing 
water, the brittleness of coal is ap- 
proached, whereas increasing water lowers 
strength and reduces brittleness. Major 
cleating in the sample is a third coal 
characteristic; however, this is very 
difficult to reproduce and is not yet 
fully refined. 

When mixing and pouring any simulated 
material, great care must be used in fol- 
lowing the recipe. Since little water is 
used, the plaster must have retarders and 
water reducers in the proper proportions 
to allow a complete and easy pour before 
the material sets up. Following this, 
the sample must be dried for about a 
month at 104° to 120° F to drive out all 
excess water and to obtain the desired 
brittleness . 



EXPERIMENTAL DESIGN 



The variability of coal and rock sam- 
ples used in cutting tests places severe 
restrictions on the design of the experi- 
ments. A standard bit (a plumb bob with 
a 60° included-angle carbide tip) is al- 
ways included in each experiment for di- 
rect comparative reference. Owing to the 
extremely variable nature of the test ma- 
terials, experimental results are treated 
as relative rather than absolute values. 

The size limitations of the sample 
blocks preclude performing an entire ex- 
periment on a single one. Since the 
blocks' responses vary, sometimes sub- 
stantially, the experimental design must 
incorporate the block differences. Block 



confounding and incomplete block designs 
are the most common methods used at TCRC 
to eliminate these effects. Hicks (_5 ) , 
Peng (8_) , and Davies (2^) provide back- 
ground for these and other methods. 
These methods do restrict the choice and 
range of variables that can be selected. 
In block confounding, the independent 
variables (e.g., cut depth, attack angle, 
bit type) must all have the same number 
of levels, i.e., there must be equal 
depths, angles, and types. With incom- 
plete block designs, only one independent 
variable can be tested in an experiment. 
An example is found in the experimental 
design for the asymmetric wear study 
(10). 



SUMMARY 



The Bureau of Mines cutting technology 
facility at TCRC has the equipment for a 
broad range of mineral fragmentation re- 
search with mechanical cutting tools. 
The equipment permits research from the 
fundamental aspects of cutter geometry 
and primary dust generation to the ap- 
plied studies of bit rotation, optimum 



depth of cut, and spacing. The facility 
is constantly changing to meet new re- 
search challenges, so the material de- 
scribed in this publication represents 
only the present situation. TCRC works 
closely on cooperative programs with in- 
dustry, and equipment is often modifiea 
to meet specific needs. 



24 



REFERENCES 



1. Black, S., B. V. Johnson, R. L. 
Schmidt, and B. Banerjee. Effect of Con- 
tinuous Miner Parameters on the Genera- 
tion of Respirable Dust. Pres. at AMC 
Min. Conv. , San Fransisco, CA, Sept. 11- 
14, 1977, and NCA/BCR Coal Conf . and Expo 
IV, Louisville, KY, Oct. 18-20, 1977; 
pub. in Min. Cong. J., v. 64, No. 4, Apr. 
1978, pp. 19-25. 

2. Davies , 0. L. The Design and 
Analysis of Industrial Experiments. Haf- 
ner, New York, 1960, 636 pp. 

3. Hanson, B. D. Cutting Parameters 
Affecting Ignition Potential for Coni- 
cal Bits. BuMines RI 8820, 1983. 



Primary Dust Generation. 
8761, 1983, 16 pp. 



BuMines RI 



11. Roepke, W. W. , and B. D. Hanson. 

New Cutting Concepts for Continuous 

Miners. Coal Min. & Process., v. 16, No. 
10, Oct. 1979, pp. 62-67. 



12. 



Testing Modified Coal Cut- 



ting Bit Designs for Reduced Energy, 
Dust, and Incendivity. BuMines RI 8801, 
1983. 

13. Roepke, W. W. , B. D. Hanson, and 
C. E. Longfellow. Drag Bit Cutting Char- 
acteristics Using Sintered Diamond In- 
serts. BuMines RI 8802, 1983. 



4. Hanson, B. D. , and W. W. Roepke. 
Effect of Symmetric Bit Wear and Attack 
Angle on Airborne Respirable Dust and En- 
ergy Consumption. BuMines RI 8395, 1979, 
24 pp. 

5. Hicks, C. R. Fundamental Concepts 
in the Design of Experiments. Rinehank & 
Winston, New York, 1964, 293 pp. 

6. Johnson, B. V., S. W. Krepela, 
and K. C. Strebig. Field Testing the 
Microminer — Research Continuous Miner. 
BuMines TPR 89, 1975, 11 pp. 

7. Larson, D. A., V. W. Dellorfano, 
C. F. Wingquist, and W. W. Roepke. Pre- 
liminary Evaluation of Bit Impact 
Ignition of Methane Using A Drum-Type 
Cutting Head. BuMines RI 8755, 1983, 23 
pp. 

8. Peng, K. C. The Design and Analy- 
sis of Scientific Experiments. Addison- 
Wesley, Reading, MA, 1967, 252 pp. 

9. Roepke, W. W. , and S. J. Anderson 
(assigned to U.S. Dept. of the Interior). 
Triangular Shaped Cutting Head for Use 
With a Longwall Mining Machine. U.S. 
Pat. 4,303,277, Dec. 1, 1981. 

10. Roepke, W. W. , and B. D. Hanson. 
Effect of Asymmetric Wear of Point At- 
:ack Bits on Coal-Cutting Parameters and 



14. Roepke, W. W. , D. P. Lindroth, and 
T. A. Myren. Reduction of Dust and Ener- 
gy During Coal Cutting Using Point-Attack 
Bits. With An Analysis of Rotary 
Cutting and Development of a New Cutting 
Concept. BuMines RI 8185, 1976, 53 pp. 

15. Roepke, W. W. , D. P. Lindroth, and 
J. W. Rasmussen (assigned to U.S. Dept. 
of the Interior) . Linear Cutting Rotary 
Head Continuous Mining Machine. U.S. 
Pat. 4,012,077, Mar. 15, 1977. 

16. Roepke, W. W. , D. P. Lindroth, and 
R. J. Wilson (assigned to U.S. Dept. of 
the Interior). Transfer by Automatic 
Face Linear Cutting Rotary Head. U.S. 
Pat. 4,062,595, Dec. 13, 1977. 

17. Roepke, W. W. , K. C. Strebig, and 
B. V. Johnson (assigned to U.S. Dept. of 
the Interior) . Method of Operating A 
Constant Depth Linear Cutting Head on a 
Retrofitted Continuous Mining Machine. 
U.S. Pat. 4,025,116, May 24, 1977. 

18. Roepke, W. W. , and J. I. Voltz. 
Coal Cutting Forces and Primary Dust 
Generation Using Radial Gage Cutters. 
BuMines RI 8800, 1983. 

19. Strebig, K. C, and H. W. Zeller. 
The Effect of Depth of Cut and Bit Type 
on the Generation of Respirable Dust. 
BuMines RI 8042, 1975, 16 pp. 



25 



APPENDIX. —SPECIFICATIONS OF MAJOR COMMERCIALLY AVAILABLE 
TEST EQUIPMENT COMPONENTS 

Small Linear Cutting Test System 

Table working surface 30 by 40 in (76.2 by 101.6 cm). 

Traverse range 24 in (60.96 cm). 

Rate range per minute 0.6 to 24 in (1.42 to 60.96 cm). 

Rate steps available 16. 

Maximum cutting force 4,000 lb (17.8 kN) . 

Maximum depth of cut 1-1/2 in (3.81 cm). 

Main drive motor 7-1/2 hp (3.81 cm). 

Net weight 5,050 lb (2,293 kg). 

Large Linear Cutting Test System 

Table working surface 40 by 128 in (101.6 by 325.1 cm). 

Traverse range 118 in (299.7 cm). 

Rate range per minute 1-15/16 to 62 in (4.92 to 157.48 cm). 

Rate steps available 16. 

Maximum cutting force Over 6,000 lb. 

Maximum depth of cut 4 in (10.16 cm). 

Main drive motor 10 hp. 

Net weight 97,000 lb (44,038 kg). 

Vertical Slotter Test System 

Ram (cutter) stroke range 3 to 22 in (7.62 to 55.88 cm). 

Cutter speed range 25 to 100 ft/min (0.76 to 3.05 m/min) 

Table diameter 28 in (71.1 cm). 

Table to lower face of ram (maximum) 44-1/2 in (113 cm). 

Table traverse — crossfeed distance (maximum). 24 in (60.96 cm). 

Table traverse — longitudinal distance 

(maximum) 32 in (81.28 cm). 



26 



Ram angular forward adjustment 0° to 10° C. 

System has an automatic rotary table 
capability. 

Maximum rated cutting force at slow speed.... 11,000 lb (48.9 kN) . 

Main drive motor 10 hp. 

Net weight 14,200 lb (6,447 kg). 

Three-Axis Dynamometer for Large Linear Cutting System 

Horizontal (tangential) and normal cutting 

forces— FZ, FY (maximum) 18,000 lb (80 kN) . 

Lateral force — FX (maximum) 2,000 lb (8.89 kN) . 

Crosstalk Less than 5 pet. 



£U.S. GOVERNMENT PRINTING OFFICE: 1983-605-015/62 



INT.-BU.OF MINES, PGH..P A. 27057 






©406 



0^ o°..l a ♦_ *C 







.o^*. V .4> ,r^. ^ 







.4T **>^'. V «° /^tfV. °- 4^ .♦>^% " 



LIBRARY OF CONGRESS 



002 959 913 









I 



